# [Bldg-sim] How to set the loop loss as 5 or 10%?

Esmireta e2fye2 at 163.com
Fri Apr 19 20:42:11 PDT 2013

```Dear Rut,
In my opinion, Q=m*cp*delta_t. During the transport of cold water, there is no mass loss, so m stay constant, and assume cp is constant. Assume the thermal loss=delta_Q, then, delta_Q=m*cp*delta_t1. Because delta_Q=10%*Q, then, delta_t1=10%*delta_t.
I think the above method is reasonable.
But why the delta_t1 will cause a lot of more energy?
Thanks!
Esmi

At 2013-04-18 21:34:52,"Rut Wattanasak" <rwattanasak at emoenergy.com> wrote:

I've come across the same scenario before.  I would say Mitchell's method is a reasonable way to go.

Additionally, the 10% loss in Temp (F) should be not equal to 10% in Thermal energy (Btu/h).  This is most likely why you see huge spike in energy consumption.  You'd have to identify the thermal property of the CHW and HW at the supply temp (in Btu/h), and determine the loss in Btu/h that is equal to 10%.  If there is no loop loss Btu/h input, you could back-calculate the reduced Btu/h in water to determine the DT.

Rut

From:bldg-sim-bounces at lists.onebuilding.org on behalf of Esmireta
Sent: Wednesday, April 17, 2013 10:25 PM
To: Mitchell Dec; BLDGSIM
Subject: Re: [Bldg-sim] How to set the loop loss as 5 or 10%?

Hi Mitchell,
I really don't know how the DT work. Why a little DT can give a huge rise in the energy consumption?
Further, will the GBCI reviewer question the way of setting DT to represent the loop loss? Did you give any specific explanation on the DT, or just leave it without narrative?
Thanks!
Esmi

At 2013-04-18 10:08:05,"Mitchell Dec" <mdec at glumac.com> wrote:
I usually run with no loss, then adjust the delta-t until the additional consumption matches the % stated by the guideline.

Mitch Dec
Glumac
Energy Department Manager

Sent from my Verizon Wireless 4G LTE Smartphone

From: "Esmireta" <e2fye2 at 163.com>
To: "BLDGSIM" <bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] How to set the loop loss as 5 or 10%?
Date: Wed, Apr 17, 2013 7:04 PM

Dear all,
As required by the district thermal energy guidance, the loop loss should be 5% for the cooling loop and 10% for the heating loop.
However, there is only DT input for the loop loss option panel. If the supply and return temperature difference is 40 F for the heating loop, the loss should be 4 F. But after I set the loss DT as 4F, the heating energy consumption will increase heavily, even 3 times of the orginal heating energy consumption.
So I wonder how it works. Does anybody have experience on it?
Thanks!
Esmi

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